The present invention generally relates to a bias circuit for an active circuit. More particularly, the present invention is directed to a dynamically adjusting bias circuit for an active circuit and multiple cascaded active circuits, which can each dynamically adapt bias. Active circuits that control RF signals, such as low-noise amplifiers (LNAs) and mixers, are crucial components in a wireless communication system. In a receiver, an RF signal is typically received from an antenna, passes to a filter, and then immediately encounters an LNA. The linearity of the LNA, therefore, significantly affects the dynamic range of the receiver. Mixers down-convert a signal from a high frequency to a low frequency by mixing the signal with a local oscillator (LO) signal. The mixer is typically positioned after the LNA and can also limit the dynamic range of the receiver. A high linearity receiver has improved immunity against strong signals and against strong interferences (i.e., jammers). That is, a high linearity receiver has less distortion (e.g., intermodulation product levels, gain compression, phase non-linearity, etc.) in the presence of strong signals or strong interferences than a low linearity receiver. Unfortunately, more DC power is required for more linearity.
High linearity, however, is not always required. In the presence of signals with normal or below signal power, active circuits can process the desired signals without distortion while operating at low bias conditions. However, to meet the linearity specification in the presence of a jamming signal, the active circuits must be properly biased to maintain linearity so as not to distort the desired signals. Such bias conditions require significantly more power than required in most situations; however, in high-risk environments, the active circuit must be able operate in the presence of jamming signals, so an unnecessarily large biasing current must be maintained. This reduces battery life, increases the heat load of the system, and reduces the lifetime of the electronic devices in the system.
Accordingly, there is a need in the art for an active circuit that can dynamically raise its bias in the presence of strong signals with minimal signal distortion and minimize power consumption by reducing the bias to the active circuit in the absence of strong signals.